#include <math.h>
main()
{
    double e=0.1,b=0.5,c,d;
      long int i;
      for (i=6; ;i*=2)
      {
        d = 1.0 - sqrt(1.0-b*b);
        b = 0.5 * sqrt(b*b+d*d);
        if ( 2*i*b-i*e<1e-15) break;
        e=b;
      }
      printf("pai=%.15lf\n",2*i*b);
      printf("The number of edges of required polygon: %ld\n",i);
}